1. Field of the Invention
The present invention relates to the novel organic compounds, a process for preparing such compounds, liquid crystal compositions having said compounds as active ingredient, and liquid crystal elements using such compositions. More particularly, the invention relates to the optically active aromatic compounds having trifluoromethyl groups useful as a primary component of ferroelectric liquid crystal compositions, a process for preparing such compounds, liquid crystal compositions having said compounds as active ingredient, and liquid crystal elements using said compositions.
2. Description of the Prior Art
A TN (twisted nematic) type display system is most popular for use in the liquid crystal display elements at present. The TN liquid crystal display elements have many advantages such as low driving voltage and small power consumption.
This type of display element, however, is inferior to the luminous type display elements such as cathode-ray tube displays, electroluminenscent displays and plasma displays in response speed. A new model of TN type display element having a twisted angle set in the range of 180.degree.-270.degree. has been developed, but this still is inferior to the luminous type display elements in response speed. Thus, in spite of many efforts made for the improvement, there has yet been realized no TN type display element with high response speed.
However a possibility of realizing marked improvement or response speed is noted in the new display system using ferroelectric liquid crystals which are being carefully studied by many researches (Clark et al: Applied Phys. Lett., 36, 899, 1980). This system makes use of a chiral smectic C phase (hereinafter referred to as Sc* phase) which shows ferroelectricity. Sc* phase is not the only phase which shows ferroelectricity. It is known that chiral smectic F phase, G phase, H phase and I phase also exhibit ferroelectricity.
The ferroelectric liquid crystal material used for the actually utilized ferroelectric liquid crystal display elements are required to meet may property requirements. At present, there is available no single compound which can meet these requirements; it is necessary for satisfying these requirements to use a ferroelectric liquid crystal composition obtained by mixing several different liquid crystal compounds or non-liquid crystal compounds.
Beside the ferroelectric liquid crystal compositions composed of ferroelectric liquid crystal compounds alone, it is reported that a ferroelectric liquid crystal composition can be obtained by using as base material a compound or a composition assuming a non-chiral smectic phase, such as non-chiral smectic C, F, G, H or I phase (hereinafter referred to as Sc phase, etc.) and mixing therewith one or more compounds assuming a ferroelectric liquid crystal phase (Japanese Patent Application Kokai (Laid-Open) No. 195187/86). A report has also been made disclosing the obtaining of a ferroelectric liquid crystal composition by using as base material a compound or composition assuming Sc phase, etc., and mixing therewith one or more compounds which don't assume a ferroelectric liquid crystal phase (Mol. Cryst. Liq. Cryst., 89, 327, 1982).
In the light of these disclosures, it is noted that there can be composed a ferroelectric liquid crystal composition by mixing one or more optically active compounds with a base material no matter whether said compounds assume a ferroelectric liquid crystal phase or not.
However, it is desirable that the optically active substance used for forming a ferroelectric liquid crystal composition is the one which assumes a liquid crystal phase, or if it does not assume a liquid crystal phase, its structure is analogous to that of the liquid crystal compounds, that is, it is a "quasi" liquid crystal substance.
For all the efforts made so far in the art, there has not yet been found any liquid crystal material which shows spontaneous polarization required for high speed response which is low in viscosity and displays a liquid crystal phase at low temperature regions.